This invention relates to tackifier resin compositions for use in adhesives and to methods for their preparation. More particularly, this invention relates to low color, aromatic-modified C5 hydrocarbon compositions prepared from piperylene concentrate and vinyl aromatic compounds and their use in adhesive applications.
Tackifier resins can be used for making thermoplastic adhesives such as hot melt adhesives (HMA) and hot melt pressure sensitive adhesives (HMPSA). A hot melt adhesive is a solid, thermoplastic material that melts quickly upon heating. A hot melt adhesive then sets to a firm bond on cooling. A hot melt pressure sensitive adhesive retains its tackiness upon cooling. Most other types of adhesives set by evaporation of a solvent or free radical curing mechanisms. Hot melt adhesives offer quick bonding making them well suited for many automated operations. The hot melt adhesives are made of elastomers, block copolymers, ethylene vinyl acetate (EVA), or amorphous polyolefins along with low molecular weight oligomer tackifiers.
A tackifier must generally be compatible with the adhesive application. Tackifiers are chosen to impart substantial adhesive strength, promote substrate wetting and generally enhance adhesive performance. Tackifiers are commonly made by polymerization of unsaturated liphatic petroleum hydrocarbon feedstocks, such as feedstock from ethylene crackers in petroleum or petrochemical processing plants.
More specifically, tackifiers are often made from unsaturated C5 hydrocarbons having two double bonds, such as C5 dienes and C5 cyclodienes. The C5 resins are commonly made using AlCl3 catalyst at a reaction temperature from about 30xc2x0 to about 70xc2x0 C. These resins have a softening point from 70xc2x0-120xc2x0 C. for adequate wetting of a substrate, for maintaining adhesive properties and for ease of packaging. These resins often, however, have a Gardner color of about 5 to about 7 or greater, which is often too dark of a color for many adhesive applications.
Reducing the amount of C5 cyclodienes in a C5 resin will generally improve or lower the Gardner color, but adhesive properties of the C5 resin may also be influenced, such as a lower softening point and reduced adhesive properties. For low color tackifiers with a reduced C5 cyclodiene content, aromatics may be added to the C5 resin to improve the resin""s adhesive characteristics. Such low cyclodiene resins often also require the use of a terpene, an unsaturated cyclic C10H16 hydrocarbon, to satisfy the adhesive requirements, such as color and softening point. See, for example, U.S. Pat. No. 4,994,516, requiring a C5 resin obtained from C5 piperylenes, unsaturated vinyl aromatics and terpenes to get adequate low color without loss of softening point. The use of terpenes, however, often require preparation of that feed stream, such as feed purification or hydrotreating prior to use, making the use of terpenes often more costly and complicated manufacturing process.
C5 resins with aromatic substitution often have high color and require post resin hydrogenation or hydrotreating. See, for example, U.S. Pat. No. 4,952,639 where C5 resins substituted with vinyl monounsaturated aromatics have dark Gardner colors from about 5 to 7 before hydrogenation and Gardner color of less than 2 after hydrogenation of the C5 resin. See also, U.S. Pat. No. 5,817,900 where hydrotreating of an aromatic-modified C5 hydrocarbon resin was required to lower the Gardner color of the resin from about 7 to about 2.
Low color C5 resins have been proposed without the use of post resin hydrogenation or hydrotreating. Such resins are, however, often limited in the amount of aromatic substitution. For example, U.S. Pat. No. 5,853,874 describes a low color, aromatic-modified C5 resin with a Gardner color of about 3, but only describes about 5 to 15 percent weight substitution of a monovinyl aromatic into the resin. Such a substitution range on monovinyl aromatic substitution limits the usefulness of these C5 resins as a tackifier in certain hot melt applications.
Other resins have been proposed with higher levels of monovinyl aromatic substitution, but require the use of a BF3 catalyst, which is less active than the more commonly used AlCl3 catalyst, resulting in increased manufacturing complexity and cost. For example, U.S. Pat. No. 5,177,163 describes low color monovinyl aromatic substituted C5 resins having at least 30 percent by weight of a monovinyl aromatic component formed with a BF3 catalyst. The BF3 catalyst, however, must be neutralized with chemicals, such as lime or NH4OH, which is more costly as compared to a water wash neutralization of the more commonly used AlCl3 catalysts. The reaction temperature necessary for low color C5 resins are about from 0xc2x0 C. to about 10xc2x0 C. with the BF3 catalysts which is generally lower than reaction temperature requirements of the AlCl3 catalyst, resulting in longer reaction times and more costly processing. Furthermore, increasing the reaction temperature of the BF3 catalyst system to more economical conditions often results in undesirable molecular weights of the resulting C5 resin.
As such there is a need for a monovinyl aromatic substituted C5 resins with low color and good adhesive qualities without the above-mentioned disadvantages of complicated or costly resin formation processing.
The present invention relates to a random copolymer hydrocarbon composition useful as a tackifier. The inventive resins are useful in hot melt adhesives and in hot melt pressure sensitive adhesives, such as with block copolymers of styrene-isoprene-styrene (SIS), block copolymers of styrene-butadiene-styrene (SBS), multiblock (SB)n where n is from 100 to 1000, amorphous polyolefins, ethylene vinyl acetate (EVA) polymers and atactic polyalpha olefins (APAO).
In one aspect of the present invention, there is provided a hydrocarbon which is a reaction product of a first predominantly C5 hydrocarbon stream containing unsaturated aliphatic monomers, such as piperylene monomers, less than about 2% weight cyclopentadiene and dicyclopentadiene monomers and less than about 1% weight isoprene, and a second hydrocarbon stream which includes a monovinyl aromatic C8 to C12 monomer. The weight ratio of said unsaturated aliphatic monomers to the monovinyl aromatic C8 to C12 monomers is from about 1.5/1 to about 6/1 to yield a unique resin having a Gardner color of less than about 4 and having a ring and ball softening point from about 85xc2x0 C. to about 100xc2x0 C. Desirably, the monovinyl aromatic C8 to C12 monomer is xcex1-methylstyrene. The inventive resin may further include from about 0 to about 15 weight percent isobutylene, isoamylene or combinations thereof. Desirably, the resin has a Mz from about 2000 to 4000 and a polydispersity of about 1.7 to about 2.0. A resin having a Mz from about 2500 to 3700 is also useful.
In another aspect of the present invention, there is provided a hydrocarbon resin which is a reaction product of a first predominantly C5 hydrocarbon stream which includes: (i) unsaturated aliphatic monomers, such as piperylene monomers; (ii) less than about 2% weight cyclopentadiene and dicyclopentadiene monomers; and (iii) less than about 1% weight isoprene; and a second hydrocarbon stream which includes a monovinyl aromatic C8 to C12 monomer. The weight ratio of the unsaturated aliphatic monomers to the monovinyl aromatic C8 to C12 monomers is desirably from about 15/1 to about 50/1. In this aspect of the invention, this resin has a Gardner color of less than about 4 and having a ring and ball softening point from about 85xc2x0 C. to about 100xc2x0 C. Desirably, the monovinyl aromatic C8 to C12 monomer is xcex1-methylstyrene. The inventive resin may further include from about 15 to about 25 weight percent isobutylene, isoamylene or combinations thereof. Desirably, the resin has a Mz from about 2500 to 4000 and a polydispersity of about 1.7 to about 2.0. A resin having a Mz from about 3000 to 3500 is also useful.
The inventive hydrocarbon copolymer resins may be prepared by (a) providing a first predominantly C5 hydrocarbon stream containing: (i) unsaturated aliphatic monomers, such as piperylene monomers; (ii) less than about 2% weight cyclopentadiene and dicyclopentadiene monomers; and (iii) less than about 1% weight isoprene; (b) providing a second hydrocarbon stream comprising a monovinyl aromatic C8 to C12 monomer; (c) combining the streams to obtain a weight ratio of the unsaturated aliphatic monomers to the monovinyl aromatic C8 to C12 monomers from about 1.5/1 to about 25/1; (d) polymerizing the combined streams at a temperature from about 25 to about 75xc2x0 C.; and (e) recovering the copolymer resin.
The inventive hydrocarbon resins may also be prepared by providing a C4 to C5 isoolefin, which is also an unsaturated aliphatic monomer. Desirably the C4 to C5 isoolefin is provided as isobutylene and the monovinyl aromatic C8 to C12 monomer is provided as xcex1-methylstyrene. In a further aspect of the present invention the isobutylene and the xcex1-methylstyrene are provided in substantially pure form, i.e., substantially free from other hydrocarbons.
The present invention is a random copolymer hydrocarbon resin useful as a tackifier. The inventive resins have low color and suitable adhesives properties for use as tackifiers in hot melt and hot melt pressure sensitive adhesives.
The inventive resins are low color, aromatic modified hydrocarbon resins. These resins are a polymerization reaction product of unsaturated aliphatic monomers and monovinyl aromatic C8 to C12 monomers. Unsaturated aliphatic monomers include, but are not limited to, isobutylene, isoprene, isoamylene (2-methyl-2-butene), trans-piperlene (trans-1,3 pentadiene), cis-piperyene (cis- 1,3 pentadiene), cyclopentadiene and dicyclopentadiene. Desirably, the amounts of cyclopentadiene and dicyclopentadiene monomers are limited to lower the Gardner color of the C5 resin. Moreover, the C5 resins of the present invention contain less than about 2 weight percent cyclopentadiene and/or dicyclopentadiene monomers. More desirably, the inventive C5 resin contains less than about 1.2 weight percent cyclopentadiene and/or dicyclopentadiene monomers.
Many of the unsaturated aliphatic monomers are provided via a concentrated piperylene stream. The concentrated piperylene stream desirably contains about 60 weight percent or more cis- and trans-piperylenes to provide, in part, a low color hydrocarbon resin. In the present invention, useful concentrated piperylene streams also contain about 1 weight percent or less isoprene and about 2 weight percent or less of cyclopentadiene and/or dicyclopentadiene. Limiting the level of the isoprene, cyclopentadiene and dicyclopentadiene in these ranges contributes to the improved lighter color of the copolymer hydrocarbon resin.
Useful monovinyl aromatic C8 to C12 monomers in the present invention include, but are not limited to, styrene, meta-methylstryene, para-methylstyrene, xcex1-methylstyrene, meta-methyl-xcex1-methylstryene, para-methyl xcex1-methylstyrene, tert-butylstyrene, and the like. In one aspect of the present invention, xcex1-methylstyrene is desired as the monovinyl aromatic C8 to C12 monomer in the inventive resins.
The inventive resins may also contain a C4 to C5 isoolefin, i.e., isobutylene or isoamylene. The inclusion of the C4 to C5 isoolefin narrows the molecular weight range of the random copolymers formed from the polymerization reaction of the unsaturated aliphatic monomers and the monovinyl aromatic C8 to C12 monomers.
In one aspect of the present invention, a hydrocarbon copolymer resin comprises a reaction product of (a) a first predominantly C5 hydrocarbon stream containing unsaturated aliphatic monomers and (b) a second hydrocarbon stream comprising a monovinyl aromatic C8 to C12 monomer. The unsaturated aliphatic monomers include a combination of (i) piperylene monomers; (ii) less than about 2% weight cyclopentadiene and/or dicyclopentadiene monomers; and (iii) less than about 1% weight isoprene. The resin has a weight ratio of the unsaturated aliphatic monomers to the monovinyl aromatic C8 to C12 monomers from about 1.5/1 to about 6/1 to yield an inventive resin having a Gardner color of less than about 4 and having a ring and ball softening point from about 85xc2x0 C. to about 100xc2x0 C.
Desirably, this resin has a Mz from about 2000 to 4000 and a polydispersity of about 1.7 to about 2.0 to impart desirable adhesive characteristics to the resin. A resin having a Mz from 2500 to 3700 is also useful as a low color resin. Unlike low-molecular weight compounds where the molecular weight in a sample is uniform, the copolymers of the present invention are polydisperse. The resins are composed of polymer chains of varying length and hence often exhibit a distribution of molecular weights. As such the resins are often characterized by different molecular weight expressions as described below:
Number average molecular weight,             M      n        =                  Σ        ⁢                  xe2x80x83                ⁢                  n          i                ⁢                  M          i                            Σ        ⁢                  xe2x80x83                ⁢                  n          i                      ,
Weight average molecular weight,
and             M      w        =                  Σ        ⁢                  xe2x80x83                ⁢                  w          i                ⁢                  M          i                            Σ        ⁢                  xe2x80x83                ⁢                  w          i                      ,
Z-average molecular weight,             M      z        =                  Σ        ⁢                  xe2x80x83                ⁢                  n          i                ⁢                  M          i          3                            Σ        ⁢                  xe2x80x83                ⁢                  n          i                ⁢                  M          i          2                      ,
where Mi is molecular weight, ni is the number of moles and wi is the weight of the i component molecules of the polymer. As used herein the term polydispersity and its variants refer to a ration of molecular weights of the resin, i.e., Mw/Mn.
Molecules of greater mass contribute more to the Mz molecular weight than do less massive molecules. The Mn molecular weight is sensitive to the presence of low-molecular weight tails. The Mz gives an indication of a high molecular weight tail in the resin and has a pronounced effect on the compatibility of the resin in an adhesive base polymer. High Mz is generally undesirable. Mw is an indication of the average molecular weight of the resin. Mn provides information on the lower molecular weight portions of the resin. The polydispersity describes the broadness of the molecular weight distribution and is the ratio of Mw/Mn. Mz, Mn, and Mw can be determined by size exclusion chromatography using a refractive index detector.
One particularly useful monovinyl aromatic C8 to C12 monomer is xcex1-methylstyrene which provides, in part, low color and good adhesive characteristics to the resin. The resin may further include from about 0 to about 15 weight percent of an isoolefin monomer, such as isobutylene, isoamylene and combinations thereof. When the isoolefin monomer is included in the reaction composition, the isoolefin monomer is considered part of the unsaturated aliphatic monomers in the above-described weight ratio of the resin.
In another aspect of the present invention, a hydrocarbon copolymer resin is prepared as a reaction product of: (a) a first predominantly C5 hydrocarbon stream containing unsaturated aliphatic monomers and (b) a second hydrocarbon stream comprising a monovinyl aromatic C8 to C12 monomer. The unsaturated aliphatic monomers include a combination of piperylene monomers, less than about 2% weight cyclopentadiene and/or dicyclopentadiene monomers and less than about 1% weight isoprene. The resin desirably has a weight ratio of unsaturated aliphatic monomers to monovinyl aromatic C8 to C12 monomers from about 15/1 to about 50/1 to yield a resin having a Gardner color of less than about 4 and having a ring and ball softening point from about 85xc2x0 C. to about 100xc2x0 C. Desirably, the resin has a Mz from about 2500 to 4000 and a polydispersity of about 1.7 to about 2.0. A resin with a Mz from about 3000 to about 3500 is also useful. This resin may further include from about 15 to about 25 weight percent of an isoolefin monomer, such as isobutylene, isoamylene and combinations thereof.
The inventive hydrocarbon copolymer resins of the present invention, which have a Gardner color of less than about 4 and having a ring and ball softening point from about 85xc2x0 C. to about 100xc2x0 C., may be prepared by (a) providing a first predominantly C5 hydrocarbon stream containing unsaturated aliphatic monomers; (b) providing a second hydrocarbon stream which includes a monovinyl aromatic C8 to C12 monomer; (c) combining the streams to obtain a weight ratio of the unsaturated aliphatic monomers to the monovinyl aromatic C8 to C12 monomers from about 1.5/1 to about 25/1; (d) polymerizing the combined streams at a temperature from about 25xc2x0 C. to about 75xc2x0 C.; and (e) recovering the copolymer resin. The unsaturated aliphatic monomers comprising a combination of piperylene monomers, cyclopentadiene and/or dicyclopentadiene monomers in amounts of about 2% less and less than about 1% weight isoprene.
In accordance with the present invention, it has been found that a useful concentrated piperylene stream desirably contains about 60 weight percent or more, cis- and trans-piperylenes to provide, in part, a low color hydrocarbon resin. As previously stated, the concentrated piperylene stream also contains about 1 weight percent or less isoprene and about 2 weight percent or less of cyclopentadiene and/or dicyclopentadiene. Limiting the levels of the isoprene, cyclopentadiene and dicyclopentadiene improves the color of the copolymer hydrocarbon resin. Desirably, the concentrated piperylene stream is a heat-soaked stream to reduce the cyclodiene content therein. During the heat-soak operation, cyclopentadiene is converted to dicyclopentadiene without substantial loss of the desirable piperylenes. The heat-soak is performed at low temperature, such as about 30xc2x0 C., for periods of time, such as up to about 6 weeks. The heat-soaked piperylene stream is then distilled to remove a substantial portion of the dicyclopentadiene. In the present invention, piperylene streams with low levels of cyclopentadiene and dicyclopentadiene, such as heat-soaked piperylene streams, form low color resins.
The piperylene stream often contains other C5 hydrocarbons, such as C5 monoolefins and C5 paraffins. The C5 monoolefins, such as but not limited to, 1-pentene, trans-2-pentene, cis-2-pentene, and cyclopentene, may react to some extent and form part of the resin copolymer. By preparing a resin with a concentrated piperylene stream, the reactive C5 monoolefins are reduced to lower levels as compared to a non-concentrated piperylene stream. Limiting the amount of reactive C5 monoolefins provides a resin prepared by the process of the present invention with a more narrow range of polydispersity. Such a narrow range of polydispersity is often desirable for compatibility of the resin with the base polymer of the adhesive. Piperylene streams are often commercially available from petroleum refining or petrochemical complexes. Such streams may result from the catalytic cracking of crude oil components or the steam cracking of light hydrocarbons. Distillation is one technique commonly used to concentrate the piperylenes from other hydrocarbons.
A useful piperylene stream for the practice of the present invention includes on a weight basis about 0.4% isoprene, about 0.8% trans-2-pentene, about 1.8% cis-2-pentene, about 6.6% 2-me-2-butene (isoamylene), about 43.3% trans-1,3-pentadiene (trans-piperylene), about 1.2% cyclopentadiene, about 23.9% cis-1,3-pentadiene (cis-piperylene), about 17.1% cyclopentene, about 3.4% cyclopentane, and about 0.1% dicyclopentadiene.
Useful monovinyl aromatic C5 to C12 monomers in the present invention include, but are not limited to, styrene, meta-methylstryene, para-methylstyrene, xcex1-methylstyrene, meta-methyl-a-methylstryene, para-methyl xcex1-methylstyrene, tert-butylstyrene, and the like. In one aspect of the present invention, an xcex1-methylstyrene stream is provided for use as the monovinyl aromatic C8 to C12 monomer in the inventive process. Desirably the ca-methylstyrene stream is substantially pure, i.e., substantially free of other monovinyl aromatic C8 to C12 monomers, unsaturated aliphatic monomers and reactive monoolefins. The use of a substantially pure xcex1-methylstyrene stream aids in the preparation of a low color resin by reducing impurities therein. Desirably, the xcex1-methylstyrene stream contains at least about 98 weight percent xcex1-methylstyrene. More desirably, the xcex1-methylstyrene stream contains at least about 99 weight percent xcex1-methylstyrene
The inventive resins may also contain a C4 to C5 isoolefin, i.e., isobutylene or isoamylene. The inclusion of the C4 to C5 isoolefins is often useful in providing a C5 resin with a narrow molecular weight range of the random copolymers formed from the polymerization reaction of the unsaturated aliphatic monomers and the monovinyl aromatic C8 to C12 monomers. A typical concentrated piperylene stream may contain some amounts of isoamylene, such as up to about 10 weight percent isoamylene. Additional amounts of C4 to C5 isoolefins may be advantageously added to the reaction mixture to control the molecular weight and polydispersity of the resin. The additional amounts of C4 to C5 isoolefins are desirably added as a substantially pure isobutylene or a pure isoamylene stream to avoid the introduction of impurities that may increase the color of the copolymer resin formed therefrom. Desirably, providing a 98 weight percent pure isobutylene or isoamylene stream facilitates the generation of low color resins. Even more desirably is a 99 weight percent pure isobutylene or isoamylene stream.
In one aspect the process of the present invention combines the unsaturated aliphatic monomer stream, the monovinyl aromatic C8 to C12 monomer stream, and the C4 to C5 isoolefin stream, if any, at a weight ratio of unsaturated aliphatic monomers, including C4 and C5 isoolefins, to the monovinyl aromatic C8 to C12 monomers in the range of from about 23/1 to about 25/1 to provide a copolymer resin with a Gardner of 4 or less, a ring and ball softening point from about 90xc2x0 C. to 100xc2x0 C., a Mz from about 2500 to about 4000 daltons and a polydispersity of about 1.7 to about 2.0.
In another aspect the process of the present invention combines the unsaturated aliphatic monomer stream, the monovinyl aromatic C8 to C12 monomer stream, and the C4 to C5 isoolefin stream, if any, at a weight ratio of unsaturated aliphatic monomers, including C4 and C5 isoolefins, to the monovinyl aromatic C8 to C12 monomers from about 3/1 to about 5/1 to yield a copolymer resin having a Gardner color of about 4 or less, a ring and ball softening point from about 85xc2x0 C. to 95xc2x0 C., a Mz from about 2700 to about 4000 daltons and a polydispersity of about 1.7 to about 2.0.
In yet another aspect of the present invention, the process of the present invention combines the unsaturated aliphatic monomer stream, the monovinyl aromatic C8 to C12 monomer stream, and the C4 to C5 isoolefin stream, if any, at a weight ratio of unsaturated aliphatic monomers, including C4 and C5 isoolefins, to the monovinyl aromatic C8 to C12 monomers from about 1.5/1to about 2.5/1 to yield a copolymer resin having a Gardner color of about 4 or less, a ring and ball softening point from about 85xc2x0 C. to 95xc2x0 C., a Mz from about 2000 to about 3800 daltons and a polydispersity of about 1.7 to about 2.0.
The resins of the present invention are desirably prepared by chemically reacting the unsaturated aliphatic monomer stream, the monovinyl aromatic C8 to C12 monomer stream, and the C4 to C5 isoolefin stream, if any, at the above-described weight ratios of unsaturated aliphatic monomers, including C4 and C5 isoolefins, to the monovinyl aromatic C8 to C12 monomers. More specifically, monomers in the streams are polymerized to form the inventive resins. Cationic polymerization of the streams is useful, but other useful polymerization techniques, such as anionic polymerization, thermal polymerization, coordination polymerization utilizing Ziegler-Natta catalysts, and the like, may also be practiced with the present invention.
In one aspect the process of the present invention includes the step of providing from about 1% to about 4% weight of a Friedel-Crafts catalyst for cationically polymerizing the reactive monomers. Desirably, the Friedel-Crafts catalyst is liquefied AlCl3/H2O/trimethylbenzene complex. A particularly useful complex has a mole ratio of AlCl3 to H2O from about 3/1 to about 7/1 and a mole ratio of trimethylbenzene to H2O from about 3/1 to about 7/1.
The process of the present invention may be conducted at any convenient reaction temperature, such as from about 0xc2x0 C. to 100xc2x0 C. A useful reaction temperature is from about 30xc2x0 C. to 70xc2x0 C. Reaction temperature of about 50xc2x0 C. is also useful.
The polymerization reaction is typically exothermic. To maintain the reaction temperature at a desirable temperature heat is often remove from a reaction vessel through a cooling mechanism, such as heat exchange equipment. Furthermore, the reaction mixture of monomers may be diluted with a solvent, such as toluene or other non-reactive hydrocarbons. Dilution of the reaction mixture with about 40 to 80 weight percent hydrocarbon solvent is useful.
The polymerization reaction is controlled in a reaction vessel, such as a batch reactor or a continuous stirred tank reactor (CSTR). The polymerization catalyst is added into the reactor to initiate catalytic polymerization. The reactor is equipped with a heat exchanger to control the reaction temperature. The average residence time in a reactor is from about 15 minutes to about several hours. The present invention is not limited to the use of a single reactor, but several reactors may be operated in series or parallel for the preparation of the inventive resins.
The reactor effluent drains into a mixer/settler combination, in which the polymer solution is washed with water. The washing and settling are done to deactivate and remove all catalyst, such as AlCl3, from the polymer solution. The polymer solution is fed into an evaporator to remove undesirable hydrocarbons, such as the hydrocarbon solvent, from the polymerization mixture by distillation under reduced pressure. The product effluent of the evaporator, in the form of a molten resin stream, is pumped to a heated receiver tank. From this tank small drops of resin are formed and solidified on a cooling belt. The solidified resin droplets are a convenient commercial form of the inventive resins.